1. Field of the Invention
The present invention generally relates to ink jet printhead apparatus and, more particularly, to a drop-on-demand type ink jet printhead having longitudinally extending sidewall actuators piezoelectrically driven by generation of either a U or UU type electric field.
2. Description of Related Art
Ink jet printing systems use the ejection of tiny droplets of ink to produce an image. The devices produce highly reproducible and controllable droplets, so that a droplet may be printed at a location specified by digitally stored image data. Most ink jet printing systems commercially available may be generally classified as either a "continuous jet" type ink jet printing system where droplets are continuously ejected from the printhead and either directed to or away from the paper depending on the desired image to be produced or as a "drop-on-demand" type ink jet printing system where droplets are ejected from the printhead in response to a specific command related to the image to be produced.
In drop-on-demand type ink jet printing systems, a volumetric change in the fluid is induced by the application of a voltage pulse to a piezoelectric material which is directly or indirectly coupled to the fluid. This volumetric change causes pressure/velocity transients to occur in the fluid and these are directed so as to produce a droplet that issues from an orifice. Recently, considerable interest has been directed to piezoelectric drop-on-demand type ink jet printheads which utilize sidewall actuators to impart droplet ejecting pressure pulses into the ink carrying channels. See, for example, U.S. Pat. Nos. 4,536,097 to Nilsson, 4,879,568 to Bartky et al., 4,887,100 to Michaelis et al. and 5,016,028 to Temple.
In Ser. No. 07/748,220, a U type drop-on-demand ink jet printhead was disclosed. The U type ink jet printhead included a lower body portion formed from an active piezoelectric material, a plurality of intermediate sections formed from an active piezoelectric material and an upper body portion formed from an inactive material. The lower body portion further included an upper side surface and a plurality of generally parallel spaced projections vertically projecting therefrom. Lower side surfaces of a plurality of intermediate sections were conductively mounted to top side surfaces of the lower body projections and the upper body portion was conductively mounted to upper side surfaces of the plurality of intermediate sections. In this manner, an ink jet printhead in which the lower body portion, the plurality of intermediate sections and the upper body portion defined a plurality of generally parallel, longitudinally extending ink ejecting channels was formed. For this ink jet printhead, the intermediate sections further defined first and second actuators and the projections and upper surface of the lower body portion defined a third actuator for each of the channels.
In Ser. No. 07/859,671, a UU type drop-on-demand ink jet printhead was disclosed. The UU type ink jet printhead included lower and upper body portions formed from an active piezoelectric material. The lower body portion further included an upper side surface and a plurality of generally parallel spaced projections vertically projecting therefrom and the upper body portion includes a lower side surface and a plurality of generally parallel space projections projecting vertically therefrom. Top side surfaces of the lower body projections were then conductively mounted to bottom side surfaces of the upper body projections to form a plurality of generally parallel, longitudinally extending channels from which ink may be ejected therefrom. In this manner, an ink jet printhead in which the projections and upper surface of the lower body portion defined a first actuator and the projections and lower surface of the upper body portion defined a second actuator for each of the channels was formed.
While representing a significant improvement over prior drop-on-demand ink jet printhead in most regards, the above-described U and UU type drop-on-demand ink jet printheads lack a certain amount of flexibility in the ability to modulate the droplet ejecting pressure wave. More specifically, because the entire length of each channel is electrically and mechanically the same, the U and UU type ink jet printheads are unable to utilize electrical and mechanical variations in the structure of the printhead to vary the shape of the pressure waves generated thereby.
It is, therefore, an object of this invention to provide enhanced U and UU type drop-on-demand ink jet printheads which incorporate electrical and/or mechanical variations in the structure thereof capable of modifying the shape of pressure waves generated thereby and consequently affect ink droplets ejected thereby in a manner which enhances the ability of the printheads to perform spot size modulation.